The present invention relates generally to a method of controlling a refrigeration system. More particularly, the invention relates to a method of controlling the start/stop of a generator that powers a refrigeration system used on containers transporting frozen goods via rail or roadway.
It is common in the field of transport refrigeration to control the start/stop of the generator and thereby, the compressor (refrigeration system) and circulating fans by monitoring the temperature of the inside of the container with an in-box temperature sensor.
In a typical system, frozen goods at 0 degrees Fahrenheit are loaded into an insulated refrigeration container destined for transit by ship, railcar or truck. Each container is supplied with its own independent refrigeration system and circulating fans. The system and fans are designed with sufficient capacity to maintain a pre-set box temperature of varying degrees F. for the duration of the trip. While on board ship, the containers can be connected to a ship's generator to provide power to the refrigeration systems. When the containers are in port, they may be connected to a power source provided by a local utility.
When, however, the containers are in transit by railcar or truck, it must have its own generator. For railcar transport, up to 10 refrigeration containers may be loaded on a single railcar and powered by one generator mounted on the same railcar. For truck transport, each container must have its own generator which is clipped directly to the container or fastened to a container chassis. The generators are usually the gas or diesel fuel-type and consume an average of 1 gallon per hour. The generator's fuel tank typically holds 130 gallons of fuel.
The refrigeration compressor automatically cycles on as the in-box temperature sensor signals the need for a reduction in temperature and off when the pre-set temperature is reached. The in-box sensor only controls the operation of the compressor. The generator is not turned off. It continues to run throughout the trip to power the circulating fans regardless of whether the compressor is on or off and regardless of the in-box temperature or the ambient temperature (the temperature outside the box).
On most cross-country rail or roadway trips, continuous operation of the generator consumes the entire 130 gallons of fuel well before the container's destination. This requires a refueling process, the man-power and fueling facilities at various points along the way. Since containers begin and end their routes from various locations, it is virtually impossible to predict where and when refueling is required. Quite often, along the route, a generator dies for lack of fuel and does not get refueled and restarted and the frozen contents of the container are at the risk of perishing.
It is well known that the circulating fans in the container have minimal effect in efficiently moving chilled air to every part of a container fully loaded with frozen goods. It is also well known that circulating fans generate a significant amount of BTUs/min., thereby counterproductively contributing to the raising of the in-box temperature. In addition, should the compressor experience failure during transit, the fans, since they are not controlled by the in-box temperature sensor, would continue to run and ultimately raise the in-box temperature to a point where the frozen goods would perish.
It is, therefore, questionable that the continuous operation of the circulating fans is justified considering: (1) the amount of fuel and expense required to operate the generator when it is operating solely to power the fans; (2) the effectiveness of the fans; (3) the fact that the fans themselves, when operating, contribute to raising the in-box temperature, thereby decreasing the overall efficiency of the refrigeration system, and; (4) the risk of loosing a load of perishable goods if the compressor were to fail in transit.
This is especially questionable, when the container is transported through an area of the country where the ambient temperature is the same as or below the required in-box temperature. In these conditions, there is no need for the circulating fans to be operating and therefore, no need for the generator to be running. While the generator is operated during this period: (1) generator running time and its associated maintenance costs, man power and fuel consumption are a total waste, and; (2) the environment is unnecessarily contaminated.
A number of devices and methods have been proposed for controlling generators. None of these, however, have addressed the serious problem of generators that are operating unnecessarily.
U.S. Pat. No. 5,977,646 to Lenz et al. discloses a method for automatically restarting a generator set following a nuisance shutdown.
U.S. Pat. No. 5,561,330 to Crook discloses an automatic electric power generator control that automatically starts the generator engine and the generator when a demand is made for electric power.
U.S. Pat. No. 4,286,683 to Zeigner et al. and U.S. Pat. No. 5,072,703 to Sutton disclose systems for automatically stopping and restarting the internal combustion engine of a vehicle.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it would be advantageous to provide an alternative device and method of limiting the running time of a generator during its transit so as to reduce fuel consumption, reduce overall operational and maintenance costs, and reduce environmental contamination while safely ensuring the goods in transit are kept frozen at the required in-box temperature.